U.S. patent application number 14/901829 was filed with the patent office on 2016-12-22 for nonaqueous electrolytic solution for electric double layer capacitor.
This patent application is currently assigned to OTSUKA CHEMICAL CO., LTD.. The applicant listed for this patent is OTSUKA CHEMICAL CO., LTD.. Invention is credited to Shoji HIKETA, Taiji NAKAGAWA, Koichi SORAJO, Yoshihisa TOKUMARU.
Application Number | 20160372274 14/901829 |
Document ID | / |
Family ID | 52143482 |
Filed Date | 2016-12-22 |
United States Patent
Application |
20160372274 |
Kind Code |
A1 |
TOKUMARU; Yoshihisa ; et
al. |
December 22, 2016 |
NONAQUEOUS ELECTROLYTIC SOLUTION FOR ELECTRIC DOUBLE LAYER
CAPACITOR
Abstract
Provided is a nonaqueous electrolytic solution that provides an
electric double layer capacitor having excellent durability. The
nonaqueous electrolytic solution is prepared by dissolving a
quaternary ammonium salt as an electrolyte in a nonaqueous solvent,
and the nonaqueous electrolytic solution comprises a
diethylpyrrolidinium salt and/or a
1-ethyl-1,3-dimethylpyrrolidinium salt.
Inventors: |
TOKUMARU; Yoshihisa;
(Tokushima, JP) ; NAKAGAWA; Taiji; (Tokushima,
JP) ; HIKETA; Shoji; (Tokushima, JP) ; SORAJO;
Koichi; (Tokushima, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
OTSUKA CHEMICAL CO., LTD. |
Osaka |
|
JP |
|
|
Assignee: |
OTSUKA CHEMICAL CO., LTD.
Osaka
JP
|
Family ID: |
52143482 |
Appl. No.: |
14/901829 |
Filed: |
June 3, 2014 |
PCT Filed: |
June 3, 2014 |
PCT NO: |
PCT/JP2014/064771 |
371 Date: |
December 29, 2015 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
Y02E 60/13 20130101;
H01G 9/155 20130101; H01G 11/60 20130101; H01G 11/64 20130101; H01G
9/035 20130101; H01G 11/62 20130101 |
International
Class: |
H01G 11/62 20060101
H01G011/62; H01G 11/60 20060101 H01G011/60 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 2, 2013 |
JP |
2013-138548 |
Claims
1. A nonaqueous electrolytic solution prepared by dissolving a
quaternary ammonium salt represented by General Formula (I):
##STR00007## (wherein X.sup.- represents a counter ion selected
from the group consisting of PF.sub.6.sup.-, BF.sub.4.sup.-,
AsF.sub.6.sup.-, N(CF.sub.3SO.sub.3).sub.2.sup.-,
N(FSO.sub.3).sub.2.sup.-, SbF.sub.6.sup.-, and RfSO.sub.3 (Rf is a
fluoroalkyl group having 1 to 8 carbon atoms)) as an electrolyte in
a nonaqueous solvent, the nonaqueous electrolytic solution
comprising: a diethylpyrrolidinium salt represented by General
Formula (II-1): ##STR00008## (wherein Y.sup.- represents a counter
ion selected from the group consisting of PF.sub.6.sup.-,
BF.sub.4.sup.-, AsF.sub.6.sup.-, N(CF.sub.3SO.sub.3).sub.2.sup.-,
N(FSO.sub.3).sub.2.sup.-, SbF.sub.6.sup.-, and RfSO.sub.3.sup.- (Rf
is a fluoroalkyl group having 1 to 8 carbon atoms) and may be the
same as or different from the counter ion (X.sup.-) contained in
General Formula (I)); and/or a 1-ethyl-1,3-dimethylpyrrolidinium
salt represented by General Formula (II-2): ##STR00009## (wherein
Z.sup.- represents a counter ion selected from the group consisting
of PF.sub.6.sup.-, BF.sub.4.sup.-, AsF.sub.6.sup.-,
N(CF.sub.3SO.sub.3).sub.2.sup.-, N(FSO.sub.3).sub.2.sup.-,
SbF.sub.6.sup.-, and RfSO.sub.3.sup.- (Rf is a fluoroalkyl group
having 1 to 8 carbon atoms) and may be the same as or different
from the counter ion (X.sup.-) contained in General Formula
(I)).
2. The nonaqueous electrolytic solution according to claim 1,
comprising the diethylpyrrolidinium salt represented by General
Formula (II-1) and/or the 1-ethyl-1,3-dimethylpyrrolidinium salt
represented by General Formula (II-2) at a concentration of 0.1 ppm
to 30,000 ppm.
3. The nonaqueous electrolytic solution according to claim 1,
comprising the diethylpyrrolidinium salt represented by General
Formula (II-1) and/or the 1-ethyl-1,3-dimethylpyrrolidinium salt
represented by General Formula (II-2) at a concentration of 1 ppm
to 20,000 ppm.
4. The nonaqueous electrolytic solution according to claim 1,
comprising the diethylpyrrolidinium salt represented by General
Formula (II-1) and/or the 1-ethyl-1,3-dimethylpyrrolidinium salt
represented by General Formula (II-2) at a concentration of 10 ppm
to 15,000 ppm.
5. The nonaqueous electrolytic solution according to claim 1,
wherein the nonaqueous electrolytic solution comprises the
diethylpyrrolidinium salt represented by General Formula (II-1)
and/or the 1-ethyl-1,3-dimethylpyrrolidinium salt represented by
General Formula (II-2) at a concentration of 50 ppm to 10,000
ppm.
6. The nonaqueous electrolytic solution according to any one of
claims 1 to 5, wherein the counter ion (X.sup.-) of the quaternary
ammonium salt represented by General Formula (I) is a fluoroborate
ion (BF.sub.4.sup.-).
7. The nonaqueous electrolytic solution according to any one of
claims 1 to 6, wherein the nonaqueous solvent is at least one
solvent selected from the group consisting of propylene carbonate,
ethylene carbonate, butylene carbonate, sulfolane, methylsulfolane,
dimethyl carbonate, ethyl methyl carbonate, and diethyl
carbonate.
8. An electric double layer capacitor comprising the nonaqueous
electrolytic solution according to any one of claims 1 to 7 as an
electrolytic solution.
Description
TECHNICAL FIELD
[0001] The present invention relates to a nonaqueous electrolytic
solution for an electric double layer capacitor and to an electric
double layer capacitor.
BACKGROUND ART
[0002] Electric double layer capacitors (EDLCs) are power storage
devices that store electric power by using a phenomenon in which
ions in an electrolytic solution form an electric double layer due
to physical adsorption to an electrode when an electric field is
applied to the electrolytic solution. As compared with secondary
batteries such as lithium-ion batteries that generate electricity
by a chemical reaction, the EDLCs have a higher charging and
discharging speed and thus are widely used in uninterruptible power
supply systems (UPSs), for example. In recent years, social demands
for environmental consciousness and energy efficiency have become
more severe, and EDLCs with the above-mentioned properties have
been more widely, increasingly demanded as temporary electric power
storage apparatuses for energy recovery and use of the energy as
auxiliary electric power in automobiles and the like and for wind
power energy, and as electric power supplies for copy machines or
similar machines to return from a standby condition. For the
reasons, EDLCs are one of the most attractive power storage
devices.
[0003] In recent years, electrochemical devices including batteries
and capacitors are required to have much higher output density and
energy density, and organic electrolytic solutions (nonaqueous
electrolytic solutions) have been more widely used than aqueous
electrolytic solutions from the viewpoint of voltage endurance.
[0004] Examples of known and widely used organic electrolytic
solutions include an electrolytic solution prepared by dissolving a
solid ammonium salt (electrolyte) such as a linear aliphatic
ammonium salt for example, a tetraethylammonium salt and a
triethylmethylammonium salt in an organic solvent such as propylene
carbonate (Patent Literature 1); and electrolytic solutions
prepared by dissolving a cyclic aliphatic ammonium salt such as an
N-ethyl-N-methyl pyrrolidinium salt (Patent Literature 2) or a
spiro-(1,1)-bipiperidinium salt (Patent Literature 3) in an organic
solvent such as propylene carbonate. However, the electrolytic
solutions have insufficient durability when used in electric double
layer capacitors. One of the reasons for the insufficient
durability is decomposition of a carbonate solvent used as the
solvent. When the carbonate solvent is decomposed, carbon monoxide
or carbon dioxide is generated and reacts with the electrolyte. The
reaction products presumably further cause complicated
decomposition reactions, deteriorating the performance of the
electrolytic solution, for example.
CITATION LIST
Patent Literature
[0005] Patent Literature 1: JP 03-58526 B
[0006] Patent Literature 2: JP 08-31401 B
[0007] Patent Literature 3: JP 2008-210871 A
SUMMARY OF INVENTION
Technical Problem
[0008] In view of the above circumstances, an object of the present
invention is to provide a nonaqueous electrolytic solution that
provides an electric double layer capacitor having excellent
durability.
Solution to Problem
[0009] As a result of intensive studies to develop an electrolyte
and an electrolytic solution for electric double layer capacitors
capable of solving the problem, the inventors of the present
invention have found that an electric double layer capacitor
produced using a nonaqueous electrolytic solution containing an
ethylmethylpyrrolidinium salt represented by General Formula (I)
and further containing a diethylpyrrolidinium salt represented by
General Formula (II-1) and/or a 1-ethyl-1,3-dimethylpyrrolidinium
salt represented by General Formula (II-2) has excellent
durability.
##STR00001##
[0010] In General Formula (I), X.sup.- represents a counter ion
selected from the group consisting of PF.sub.6.sup.-,
BF.sub.4.sup.-, AsF.sub.6.sup.-, N(CF.sub.3SO.sub.3).sub.2.sup.-,
N(FSO.sub.3).sub.2.sup.-, SbF.sub.6.sup.-, and RfSO.sub.3 (Rf is a
fluoroalkyl group having 1 to 8 carbon atoms).
##STR00002##
[0011] In General Formula (II-1), Y.sup.- represents a counter ion
selected from the group consisting of PF.sub.6.sup.-,
BF.sub.4.sup.-, AsF.sub.6.sup.-, N(CF.sub.3SO.sub.3).sub.2.sup.-,
N(FSO.sub.3).sub.2.sup.-, SbF.sub.6.sup.-, and RfSO.sub.3.sup.- (Rf
is a fluoroalkyl group having 1 to 8 carbon atoms) and may be the
same as or different from the counter ion (X.sup.-) contained in
General Formula (I)
##STR00003##
[0012] In General Formula (II-2), Z.sup.- represents a counter ion
selected from the group consisting of PF.sub.6.sup.-,
BF.sub.4.sup.-, AsF.sub.6.sup.-, N(CF.sub.3SO.sub.3).sub.2.sup.-,
N(FSO.sub.3).sub.2.sup.-, SbF.sub.6.sup.-, and RfSO.sub.3.sup.- (Rf
is a fluoroalkyl group having 1 to 8 carbon atoms) and may be the
same as or different from the counter ion (X.sup.-) contained in
General Formula (I).
[0013] That is, the present invention encompasses the following
aspects.
(1) A nonaqueous electrolytic solution prepared by dissolving a
quaternary ammonium salt represented by General Formula (I):
##STR00004##
[0014] (wherein X.sup.- represents a counter ion selected from the
group consisting of PF.sub.6.sup.-, BF.sub.4.sup.-,
AsF.sub.6.sup.-, N(CF.sub.3SO.sub.3).sub.2.sup.-,
N(FSO.sub.3).sub.2.sup.-, SbF.sub.6.sup.-, and RfSO.sub.3 (Rf is a
fluoroalkyl group having 1 to 8 carbon atoms)) as an electrolyte in
a nonaqueous solvent, the nonaqueous electrolytic solution
comprising:
[0015] a diethylpyrrolidinium salt represented by General Formula
(II-1):
##STR00005##
[0016] (wherein Y.sup.- represents a counter ion selected from the
group consisting of PF.sub.6.sup.-, BF.sub.4.sup.-,
AsF.sub.6.sup.-, N(CF.sub.3SO.sub.3).sub.2.sup.-,
N(FSO.sub.3).sub.2.sup.-, SbF.sub.6.sup.-, and RfSO.sub.3.sup.- (Rf
is a fluoroalkyl group having 1 to 8 carbon atoms) and may be the
same as or different from the counter ion (X.sup.-) contained in
General Formula (I)); and/or
[0017] a 1-ethyl-1,3-dimethylpyrrolidinium salt represented by
General Formula (II-2):
##STR00006##
[0018] (wherein Z.sup.- represents a counter ion selected from the
group consisting of PF.sub.6.sup.-, BF.sub.4.sup.-,
AsF.sub.6.sup.-, N(CF.sub.3SO.sub.3).sub.2.sup.-,
N(FSO.sub.3).sub.2.sup.-, SbF.sub.6.sup.-, and RfSO.sub.3.sup.- (Rf
is a fluoroalkyl group having 1 to 8 carbon atoms) and may be the
same as or different from the counter ion (X.sup.-) contained in
General Formula (I)).
(2) The nonaqueous electrolytic solution according to the above
(1), comprising the diethylpyrrolidinium salt represented by
General Formula (II-1) and/or the 1-ethyl-1,3-dimethylpyrrolidinium
salt represented by General Formula (II-2) at a concentration of
0.1 ppm to 30,000 ppm. (3) The nonaqueous electrolytic solution
according to the above (1), comprising the diethylpyrrolidinium
salt represented by General Formula (II-1) and/or the
1-ethyl-1,3-dimethylpyrrolidinium salt represented by General
Formula (II-2) at a concentration of 1 ppm to 20,000 ppm. (4) The
nonaqueous electrolytic solution according to the above (1),
comprising the diethylpyrrolidinium salt represented by General
Formula (II-1) and/or the 1-ethyl-1,3-dimethylpyrrolidinium salt
represented by General Formula (II-2) at a concentration of 10 ppm
to 15,000 ppm. (5) The nonaqueous electrolytic solution according
to the above (1), wherein the nonaqueous electrolytic solution
comprises the diethylpyrrolidinium salt represented by General
Formula (II-1) and/or the 1-ethyl-1,3-dimethylpyrrolidinium salt
represented by General Formula (II-2) at a concentration of 50 ppm
to 10,000 ppm. (6) The nonaqueous electrolytic solution according
to any one of the above (1) to (5), wherein the counter ion
(X.sup.-) of the quaternary ammonium salt represented by General
Formula (I) is a fluoroborate ion (BF.sub.4.sup.-). (7) The
nonaqueous electrolytic solution according to any one of the above
(1) to (6), wherein the nonaqueous solvent is at least one solvent
selected from the group consisting of propylene carbonate, ethylene
carbonate, butylene carbonate, sulfolane, methylsulfolane, dimethyl
carbonate, ethyl methyl carbonate, and diethyl carbonate. (8) An
electric double layer capacitor comprising the nonaqueous
electrolytic solution according to any one of the above (1) to (7)
as an electrolytic solution.
Advantageous Effects of Invention
[0019] Using the nonaqueous electrolytic solution of the present
invention, a highly durable electric double layer capacitor that
exhibits less capacity decrease (capacity reduction) and less
resistance increase over a long period of time can be produced.
DESCRIPTION OF EMBODIMENTS
[0020] The present invention will now be described in detail.
[0021] The nonaqueous electrolytic solution of the present
invention is a nonaqueous electrolytic solution prepared by
dissolving a quaternary ammonium salt represented by General
Formula (I) as an electrolyte in a nonaqueous solvent. The
nonaqueous electrolytic solution of the present invention comprises
a diethylpyrrolidinium salt represented by General Formula (II-1)
and/or a 1-ethyl-1,3-dimethylpyrrolidinium salt represented by
General Formula (II-2).
[0022] In the present specification, the quaternary ammonium salt
represented by General Formula (I) is also called
ethylmethylpyrrolidinium salt (I). The diethylpyrrolidinium salt
represented by General Formula (II-1) and the
1-ethyl-1,3-dimethylpyrrolidinium salt represented by General
Formula (II-2) are also called diethylpyrrolidinium salt (II-1) and
1-ethyl-1,3-dimethylpyrrolidinium salt (II-2), respectively.
[0023] The diethylpyrrolidinium salt (II-1) and the
1-ethyl-1,3-dimethylpyrrolidinium salt (II-2) are used in order to
improve the durability of an electric double layer capacitor. The
diethylpyrrolidinium salt (II-1) and/or the
1-ethyl-1,3-dimethylpyrrolidinium salt (II-2) contained in the
nonaqueous electrolytic solution together with the
ethylmethylpyrrolidinium salt (I) and the nonaqueous solvent can
effectively control the capacity decrease and the resistance
increase of an electric double layer capacitor produced using the
nonaqueous electrolytic solution and can improve the durability of
the electric double layer capacitor. In the nonaqueous electrolytic
solution, the upper limit of the concentration of the
diethylpyrrolidinium salt (II-1) and/or the
1-ethyl-1,3-dimethylpyrrolidinium salt (II-2) is preferably about
30,000 ppm, more preferably about 20,000 ppm, even more preferably
about 15,000 ppm, particularly preferably about 10,000 ppm, and
most preferably about 6,000 ppm. In the nonaqueous electrolytic
solution, the lower limit of the concentration of the
diethylpyrrolidinium salt (II-1) and/or the
1-ethyl-1,3-dimethylpyrrolidinium salt (II-2) is preferably about
0.1 ppm, more preferably about 1 ppm, even more preferably about 10
ppm, and particularly preferably about 50 ppm.
[0024] The nonaqueous electrolytic solution of the present
invention comprises the diethylpyrrolidinium salt (II-1) and/or the
1-ethyl-1,3-dimethylpyrrolidinium salt (II-2) at a concentration of
preferably 0.1 ppm to 30,000 ppm, more preferably 1 ppm to 20,000
ppm, even more preferably 10 ppm to 15,000 ppm, and particularly
preferably 50 ppm to 10,000 ppm.
[0025] When a nonaqueous electrolytic solution comprises the
diethylpyrrolidinium salt (II-1) and/or the
1-ethyl-1,3-dimethylpyrrolidinium salt (II-2), an electric double
layer capacitor produced using the nonaqueous electrolytic solution
has excellent durability.
[0026] The reason of the improved durability of the electric double
layer capacitor produced using the nonaqueous electrolytic solution
containing the diethylpyrrolidinium salt (II-1) and/or the
1-ethyl-1,3-dimethylpyrrolidinium salt (II-2) is unclear, but these
substances presumably form an SEI film on the electrode to suppress
the decomposition of the electrolytic solution.
[0027] In the present invention, the ethylmethylpyrrolidinium salt
represented by General Formula (I) is typically used as the
electrolyte. The counter ion (anion) (X.sup.-) in General Formula
(I) is preferably a fluoroborate ion (BF.sub.4.sup.-).
[0028] The concentration of the ethylmethylpyrrolidinium salt (I)
in the nonaqueous electrolytic solution is preferably about 0.1 to
3 mol/L and particularly preferably about 0.5 to 1.5 mol/L. When
the concentration of the ethylmethylpyrrolidinium salt (I) is
within this range, the nonaqueous electrolytic solution has high
conductivity, and thus such a range is preferred. In addition, when
the electrolyte concentration is within such a range, the increase
in internal resistance of an electric double layer capacitor
produced using the nonaqueous electrolytic solution can be more
effectively controlled. Furthermore, when the electrolyte
concentration is within such a range, salt precipitation in the
nonaqueous electrolytic solution does not occur even at low
temperatures, and thus such a range is preferred.
[0029] In the diethylpyrrolidinium salt represented by General
Formula (II-1), the counter ion (anion) (Y.sup.-) may be the same
as or different from the counter ion (X.sup.-) contained in General
Formula (I). The counter ion (Y.sup.-) is preferably a fluoroborate
ion (BF.sub.4.sup.-). The diethylpyrrolidinium salt represented by
General Formula (II-1) is preferably diethylpyrrolidinium
tetrafluoroborate.
[0030] In the 1-ethyl-1,3-dimethylpyrrolidinium salt represented by
General Formula (II-2), the counter ion (anion) (Z.sup.-) may be
the same as or different from the counter ion (X.sup.-) contained
in General Formula (I). The counter ion (Z.sup.-) in the General
Formula (II-2) is preferably a fluoroborate ion (BF.sub.4.sup.-).
The 1-ethyl-1,3-dimethylpyrrolidinium salt represented by General
Formula (II-2) is preferably 1-ethyl-1,3-dimethylpyrrolidinium
tetrafluoroborate.
[0031] When the nonaqueous electrolytic solution comprises the
ethylmethylpyrrolidinium salt (I), the diethylpyrrolidinium salt
(II-1), and the 1-ethyl-1,3-dimethylpyrrolidinium salt (II-2), the
counter ion (X.sup.-) in the General Formula (I), the counter ion
(Y.sup.-) in General Formula (II-1), and the counter ion (Z.sup.-)
in General Formula (II-2) may be all the same or different.
[0032] Each of the ethylmethylpyrrolidinium salt (I), the
diethylpyrrolidinium salt (II-1), and the
1-ethyl-1,3-dimethylpyrrolidinium salt (II-2) may be a commercially
available compound. Also, the compounds can be produced by the
method described in JP 08-31401 B, for example.
[0033] The nonaqueous solvent used in the electrolytic solution is
not particularly limited and is exemplified by ethylene carbonate,
propylene carbonate, butylene carbonate, ethyl methyl carbonate,
dimethyl carbonate, diethyl carbonate, .gamma.-butyrolactone,
acetonitrile, sulfolane, and methylsulfolane. These solvents may be
used alone or as a mixture of two or more thereof. The nonaqueous
solvent is preferably at least one solvent selected from the group
consisting of propylene carbonate, ethylene carbonate, butylene
carbonate, sulfolane, methylsulfolane, dimethyl carbonate, ethyl
methyl carbonate, and diethyl carbonate. The nonaqueous solvent is
particularly preferably propylene carbonate. As the nonaqueous
solvent, a commercially available solvent may be used as it is or
after further purified by distillation or another method as
necessary.
[0034] The method for producing the nonaqueous electrolytic
solution comprising the diethylpyrrolidinium salt (II-1) and/or the
1-ethyl-1,3-dimethylpyrrolidinium salt (II-2) is not particularly
limited. Also, the method for controlling the concentration of the
diethylpyrrolidinium salt (II-1) and/or the
1-ethyl-1,3-dimethylpyrrolidinium salt (II-2) in the nonaqueous
electrolytic solution is not particularly limited. For example, by
adjusting the amount of diethylpyrrolidinium salt (II-1) and/or the
1-ethyl-1,3-dimethylpyrrolidinium salt (II-2) in the electrolyte
(the ethylmethylpyrrolidinium salt (I)) as the raw material of the
nonaqueous electrolytic solution, the content of these compounds in
the resulting nonaqueous electrolytic solution can be adjusted.
Alternatively, the diethylpyrrolidinium salt (II-1) and/or the
1-ethyl-1,3-dimethylpyrrolidinium salt (II-2) may be separately
added to a nonaqueous electrolytic solution. For example, when the
electrolyte (namely, the ethylmethylpyrrolidinium salt (I)) as the
raw material of the nonaqueous electrolytic solution comprises the
diethylpyrrolidinium salt (II-1) or the
1-ethyl-1,3-dimethylpyrrolidinium salt (II-2) at a high content,
the content of such a compound in the nonaqueous electrolytic
solution can be adjusted by the following method, for example. More
specifically, for example, when a nonaqueous electrolytic solution
that is prepared by dissolving the ethylmethylpyrrolidinium salt
(I) as the electrolyte in the nonaqueous solvent so as to give a
concentration of about 0.5 to 1.5 mol/L comprises the
diethylpyrrolidinium salt (II-1) and/or the
1-ethyl-1,3-dimethylpyrrolidinium salt (II-2) at a concentration of
more than 30,000 ppm, a solvent having high solubility of the
diethylpyrrolidinium salt (II-1) and/or the
1-ethyl-1,3-dimethylpyrrolidinium salt (II-2) is used to
recrystallize the electrolyte. Subsequent filtration can remove an
appropriate amount of the diethylpyrrolidinium salt (II-1) and/or
the 1-ethyl-1,3-dimethylpyrrolidinium salt (II-2). The purified
electrolyte is then dissolved in the nonaqueous solvent. In this
way, the solvent used for the crystallization is removed and as a
result a nonaqueous electrolytic solution comprising a reduced
amount of the diethylpyrrolidinium salt (II-1) and/or the
1-ethyl-1,3-dimethylpyrrolidinium salt (II-2) can be obtained. The
content of the diethylpyrrolidinium salt (II-1) and the
1-ethyl-1,3-dimethylpyrrolidinium salt (II-2) controlled by this
operation typically depends on the solvent used for the
crystallization and the crystallization temperature. For example,
the electrolyte is dissolved in butanol at about 60 to 105.degree.
C. and then subjected to recrystallization; and the crystal is
collected by filtration and then is dissolved again in a nonaqueous
solvent to remove the crystallization solvent. By this operation,
the content of the diethylpyrrolidinium salt (II-1) and/or the
1-ethyl-1,3-dimethylpyrrolidinium salt (II-2) can be controlled to
achieve about 0.1 ppm to 30,000 ppm in the nonaqueous electrolytic
solution. When the nonaqueous electrolytic solution comprises the
diethylpyrrolidinium salt (II-1) and/or the
1-ethyl-1,3-dimethylpyrrolidinium salt (II-2) at about less than
0.1 ppm, the diethylpyrrolidinium salt (II-1) and/or the
1-ethyl-1,3-dimethylpyrrolidinium salt (II-1) can be added to
adjust the concentration to an appropriate value.
[0035] The concentration of the diethylpyrrolidinium salt (II-1)
and the 1-ethyl-1,3-dimethylpyrrolidinium salt (II-2) contained in
the nonaqueous electrolytic solution can be determined by a known
method such as ion chromatography. For example, when the
concentration is determined by ion chromatography, the conditions
described in Examples may be employed.
[0036] The electrolytic solution of the present invention may
comprise one or more components in addition to the
ethylmethylpyrrolidinium salt (I), the ethyl pyrrolidinium salt
(II-1), and the 1-ethyl-1,3-dimethylpyrrolidinium salt (II-2) as
long as the advantageous effects of the invention are achieved.
[0037] An electric double layer capacitor comprising the nonaqueous
electrolytic solution as an electrolytic solution is also
encompassed in the present invention.
[0038] The electric double layer capacitor of the present invention
can be any electric double layer capacitor that comprises the
nonaqueous electrolytic solution as the electrolytic solution, and
the production method therefor and the like are not particularly
limited. The electric double layer capacitor of the present
invention comprising the nonaqueous electrolytic solution is a
highly durable electric double layer capacitor that exhibits less
capacity decrease (capacity reduction) and less resistance
increase.
EXAMPLES
[0039] The present invention will next be described in further
detail with reference to Examples, but the invention is not limited
to these Examples.
[0040] The concentration of a diethylpyrrolidinium salt in each
nonaqueous electrolytic solution (hereinafter simply called
electrolytic solution) prepared in Examples 1 to 5 and Comparative
Example 1 and properties of the electric double layer capacitors
produced using the electrolytic solutions were determined by the
following methods.
[0041] Quantitative Determination of Diethylpyrrolidinium Salt:
[0042] Measurement was carried out by ion chromatography.
Column: Dionex Ion Pac CS14, o4.times.250 mm (Nippon Dionex)
[0043] Detection method: electric conductivity Suppressor: CSRS300
(product name, Nippon Dionex) Suppressor current value: 35 mA
Mobile phase: 0.010 M methanesulfonic acid solution Regeneration
solution: ultrapure water (2 mL/min) Mobile phase flow rate: 1.0
mL/min Column temperature: 30.degree. C. Cell temperature:
35.degree. C. Sample injection volume: 25 mL
[0044] Sample Preparation Method:
[0045] Preparation method of reference standard (solution at about
10 ppm): About 16.8 mg of diethylpyrrolidinium tetrafluoroborate
was accurately weighed and dissolved in ultrapure water to give a
100-mL solution. From the solution, 5 mL was taken out and was
diluted with ultrapure water to give a 50-mL solution.
[0046] Sample solution: About 500 mg of a sample was diluted with
ultrapure water to give a 50-mL solution.
[0047] Measurement method: The reference standard and the sample
solutions were analyzed. From the obtained peaks, the contents were
calculated in accordance with the following calculation
expression.
Diethylpyrrolidinium salt content (ppm)=peak area of
diethylpyrrolidinium salt in sample solution.times.0.01
(mg/mL).times.50 (mL)/sample amount (mg)/peak area of K.sup.+ in
standard solution.times.1,000,000 (ppm)
[0048] Properties of Electric Double Layer Capacitor
(Method for Producing Capacitor)
[0049] A device (3 cm.times.5 cm: 5 pieces were stacked) was
produced using the following materials and was subjected to vacuum
drying at 180.degree. C. for 15 hours. The device was then
impregnated with an electrolytic solution (electrolytic solution
amount: 0.097 cc/F), yielding a laminate cell (electric double
layer capacitor). The produced electric double layer capacitor was
subjected to aging treatment for 24 hours while a voltage of 2.7 V
was applied to the capacitor at room temperature, and the
respective initial properties were determined.
[0050] Electrode: a sheet electrode purchased from Japan
Gore-Tex
[0051] Electrolytic paper (separator): TF4050 manufactured by
Nippon Kodoshi
[0052] Electrolytic solution: the electrolytic solutions prepared
in Examples 1 to 5 and Comparative Example 1
[0053] The initial capacity and the internal resistance of the
electric double layer capacitor were determined with an applied
voltage of 2.7 V. After storage at 60.degree. C. for 2,000 hours
with an applied voltage of 2.7 V, the capacity was determined, and
the capacity reduction rate relative to the initial capacity was
calculated. The internal resistance was determined by an
alternating-current two-terminal method at a frequency of 1
kHz.
[0054] The method for preparing each electrolytic solution of
Examples 1 to 5 and Comparative Example 1 was as described below.
The propylene carbonate used in Examples and Comparative Example
was a superfractionated, highly pure propylene carbonate (purity:
99.99%, analyzed by GC).
Comparative Example 1
[0055] An electrolytic solution was prepared by dissolving, at room
temperature, in a dry nitrogen atmosphere with a dew point of
-40.degree. C., N-ethyl-N-methyl pyrrolidinium tetrafluoroborate as
the electrolyte in a highly pure propylene carbonate so as to give
a concentration of 1.5 mol/L. Diethylpyrrolidinium
tetrafluoroborate was not detected (undetectable) in the
electrolytic solution. Table 1 shows the properties of the electric
double layer capacitor produced using the electrolytic
solution.
Examples 1 to 5
[0056] To the electrolytic solution prepared in Comparative Example
1, diethylpyrrolidinium tetrafluoroborate was uniformly dissolved,
giving electrolytic solutions containing diethylpyrrolidinium
tetrafluoroborate at corresponding concentrations shown in Table 1.
Table 1 shows the properties of the electric double layer
capacitors produced using the respective electrolytic
solutions.
TABLE-US-00001 TABLE 1 Initial properties and durability test
results of capacitors produced using electrolytic solutions
Diethyl- pyrrolidinium tetrafluoro- Properties of electric double
layer capacitor borate Initial Initial Capacity Resistance
concentration capacity resistance reduction change (ppm) (F) (m
.OMEGA.) rate (%) rate (%) Example 1 1010 18.2 32.6 -9.0 100
Example 2 5035 18.1 32.7 -8.7 101 Example 3 10000 18.1 32.7 -8.7
100 Example 4 98 18.1 32.5 -8.9 103 Example 5 20150 17.6 34.0 -14.8
120 Compar N.D. 18.2 32.5 -15.5 147 ative- Example 1 The solvent
used was propylene carbonate (PC). The concentration of
diethylpyrrolidinium tetrafluoroborate was determined by ion
chromatography.
[0057] The results shown in Table 1 indicate that the electric
double layer capacitors produced using the respective electrolytic
solutions comprising the diethylpyrrolidinium salt in Examples 1 to
5 were highly durable and exhibited less capacity decrease
(capacity reduction) and less resistance increase as compared with
the electric double layer capacitor produced using the electrolytic
solution comprising no diethylpyrrolidinium salt in Comparative
Example 1.
[0058] The concentration of the 1-ethyl-1,3-dimethylpyrrolidinium
salt in each electrolytic solution prepared in Examples 6 to 9 and
Comparative Example 2 and properties of the electric double layer
capacitors produced using the electrolytic solutions were
determined by the following methods.
Quantitative determination of 1-ethyl-1,3-dimethylpyrrolidinium
salt
[0059] Measurement was carried out by ion chromatography. The
apparatus and measurement conditions used for the measurement were
the same as the apparatus and the conditions in the above
quantitative determination of the diethylpyrrolidinium salt.
[0060] Sample Preparation Method:
[0061] Preparation method of reference standard (solution at about
10 ppm): About 16.8 mg of 1-ethyl-1,3-dimethylpyrrolidinium
tetrafluoroborate was accurately weighed and dissolved in ultrapure
water to give a 100-mL solution in a volumetric flask. From the
solution, 5 mL was taken out and was diluted with ultrapure water
to give a 50-mL solution in a volumetric flask.
[0062] Sample solution: About 500 mg of a sample was dissolved in
ultrapure water to give a 50-mL solution in a volumetric flask.
[0063] Measurement method: The reference standard and the sample
solutions were analyzed. From the obtained peaks, the contents were
calculated in accordance with the following calculation
expression.
1-Ethyl-1,3-dimethylpyrrolidinium content (ppm)=peak area of
1-ethyl-1,3-dimethylpyrrolidinium salt in sample
solution.times.0.01 (mg/mL).times.50 (mL)/sample amount (mg)/peak
area of K.sup.+ in standard solution.times.1,000,000 (ppm)
[0064] Properties of Electric Double Layer Capacitor
[0065] Electric double layer capacitors were produced and evaluated
in the same manner as in the above except that the respective
electrolytic solutions prepared in Examples 6 to 9 and Comparative
Example 2 were used as the electrolytic solution.
Comparative Example 2
[0066] An electrolytic solution was prepared by dissolving, at room
temperature, in a dry nitrogen atmosphere with a dew point of
-40.degree. C., 1-ethyl-1-methyl pyrrolidinium tetrafluoroborate as
the electrolyte in a highly pure propylene carbonate so as to give
a concentration of 1.5 mol/L. Diethylpyrrolidinium
tetrafluoroborate was not detected (undetectable) in the
electrolytic solution. Table 2 shows the properties of the electric
double layer capacitor produced using the electrolytic
solution.
Examples 6 to 9
[0067] To the electrolytic solution prepared in Comparative Example
2, 1-ethyl-1,3-dimethylpyrrolidinium tetrafluoroborate was
uniformly dissolved, giving electrolytic solutions containing
1-ethyl-1,3-dimethylpyrrolidinium tetrafluoroborate at
corresponding concentrations shown in Table 2. Table 2 shows the
properties of the electric double layer capacitors produced using
the respective electrolytic solutions.
TABLE-US-00002 TABLE 2 Initial properties and durability test
results of capacitors produced by using electrolytic solutions
1-Ethyl-1,3- dimethyl pyrrolidinium Properties of electric double
layer tetrafluoro- capacitor borate Initial Initial Capacity
Resistance concentration capacity resistance reduction change (ppm)
(F) (m .OMEGA.) rate (%) rate (%) Example 6 1050 18.2 32.5 -9.0 100
Example 7 5200 18.1 32.4 -9.1 101 Example 8 105 18.1 32.5 -8.8 103
Example 9 20060 17.7 34.0 -14.3 125 Compar- N.D. 18.1 32.5 -15.1
150 ative Example 2 The solvent used was propylene carbonate (PC).
The concentration of 1-ethyl-1,3-dimethylpyrrolidinium
tetrafluoroborate was determined by ion chromatography.
[0068] The results shown in Table 2 indicate that the electric
double layer capacitors produced using the respective electrolytic
solutions comprising the 1-ethyl-1,3-dimethylpyrrolidinium salt in
Examples 6 to 9 were highly durable and exhibited less capacity
decrease (capacity reduction) and less resistance increase as
compared with the electric double layer capacitor produced using
the electrolytic solution comprising no
1-ethyl-1,3-dimethylpyrrolidinium salt in Comparative Example
2.
* * * * *